


Assumption Game

by pjsta



Category: Haikyuu!!
Genre: Gen, M/M, Polyamory, Rarepair, and this is the result, bit of fun, in which everyone makes assumptions that turn out to be very wrong, no actual cheating happens in this fic, so its all good
Language: English
Status: Completed
Published: 2019-05-03
Updated: 2019-05-03
Packaged: 2020-02-16 14:57:12
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,337
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18693766
Author URL: https://archiveofourown.org/users/pjsta/pseuds/pjsta
Summary: Everyone thinks Tsukishima and Yamaguchi are dating, so much so that by the time they reach high school they’ve given up trying to convince their peers otherwise. Besides, they know where they stand in their relationship, and that’s all they really need.But when they find themselves forming crushes, they begin to run into difficulties.Because they didn’t form crushes on each other. They formed crushes on other people, and now everyone thinks they’re cheating on each other.What a mess.





	Assumption Game

**Author's Note:**

> This idea kinda came out of nowhere, and I just... took it and ran with it? And this is the result.
> 
> Hope you enjoy!

People started to assume that they were dating somewhere around the time they turned twelve.

By that point, the pair of them were a package deal, and everyone knew it. So much so that when they moved up to junior high, anyone who had been at their old school knew to expect them as a pair. Knowledge which then got spread to their new classmates.

But somewhere along the line, _they’re best friends_ got changed to _they’re boyfriends_ and no matter how much they insisted otherwise, neither Yamaguchi nor Kei could get it to switch back.

Eventually, they gave up trying.

 _They_ knew where they stood in their relationship, and that was the important thing.

It also meant that Yamaguchi was less likely to get bothered by people coming up to ask about Kei’s love life, which was a plus for both of them.

When they went to Karasuno, the assumption that they were a couple went with them again. Only the students new to them were interested in trying for one of them, and usually went for Kei. Thankfully, most of them were quickly dissuaded when told by others that “ _Tsukishima-san’s been dating Yamaguchi-san since at least junior high_ ”.

Even the volleyball team were taken in with the assumption.

No one questioned how Yamaguchi could manipulate Kei in a way that others couldn’t, or how they’d frequently stay over at each other’s houses - details of which Yamaguchi happily shared with the rest of the team, or how they both had copious amounts of knowledge and blackmail on each other, or how Yamaguchi never took him seriously whenever Kei told him to shut up. To the team, that was just how their relationship worked, and probably had done for years.

Their supposedly _romantic_ relationship.

Neither of them bothered to correct them, but they didn’t confirm it either.

Besides, it _did_ help them keep annoying interested parties at bay.

 

 

They found the flaw in their plan during the summer training camps.

And somehow, it was _Kei’s_ fault, of all people.

Well, not entirely his fault.

Kuroo, Bokuto and Akaashi all had an unwitting equal part in it, so Kei _refused_ to take sole responsibility.

It wasn’t _his_ fault that the three of them had wormed their way under his skin and left him with a crush on each of them. A crush that grew more and more out of control the longer he was in contact with them.

After spending most of the week with them during their second Tokyo camp, he’d been added to a group chat with the three of them. He didn’t always respond, but he’d found himself always making sure he was up to date with it. Occasionally, they sent pictures and videos to the chat, either memes or the respective animals of their school mascots, or images of themselves.

It was after seeing a recording sent to the chat by Kuroo of Akaashi and Bokuto practicing, with the camera zooming in and paying close attention to their muscles - in particular Bokuto’s arms - that Kei knew he was in too deep. When the lunch bell rang, he collapsed into the seat next to Yamaguchi’s desk, crashed his head into his arms and groaned. In the middle of their classroom, where anyone could see.

Yamaguchi didn’t stop teasing him for _weeks_.

Kei tried to limit his contact with them, but it ended up just making things worse. He couldn’t stop thinking about them. He kept itching to open up the group chat. And then they figured out that he was trying to avoid them.

He stopped trying to avoid them.

There was no way he was going to put up with them acting all melodramatic over it, and it wasn’t like it had helped at all anyway.

By the time their next training camp arrived, Kei was under strict instructions from Yamaguchi to ask them out. Any or all of them. Kei considered asking them separately, but when he tried to choose, he found he couldn’t. He wanted all of them.

Then, in a break during individual practice in an empty gym, Akaashi asked what his relationship was with Yamaguchi.

“Is it true you’ve been dating since middle school?”

The first thing Kei thought was _It’s gotten earlier?_ Last he’d checked, the rumours had them starting dating in junior high.

The second was _thank God the other two have gone to the bathroom._ It would have been a _nightmare_ having this conversation with them snorting away in the background.

Then, he remembered that Akaashi needed an answer.

“No,” he replied, “Yamaguchi and I have never dated.” Akaashi blinked in surprise.

“Oh. I was under the impression that -”

“A common occurrence,” Kei said. Akaashi raised his eyebrow.

“Oh?”

“The rumours that we’re dating started up in junior high,” Kei explained, “and haven’t stopped since. It got to a point where it was easier to just ignore them. Besides, it means neither of us get bothered by people trying to ask us out when we aren’t interested in them.”

Something complicated flickered across Akaashi’s face then. Kei couldn’t read it. For all he was good at figuring out an opponent’s next move, he still couldn’t read people and their emotions.

“I see,” he said at last. He seemed to decide something.

“Is there anyone you’d be interested in?” Kei tried not to let his face burn too much.

 _There are three of them_ , he thought. How could he tell Akaashi that without chasing him away?

“There is,” he said slowly, “A few of them.”

“Do I know them?”

“Yes.”

 _It’s you,_ Kei thought, _It’s you and Kuroo and Bokuto but I’d rather not say anything at all than risk losing any of you._

“Your team?”

“... No.” Something else flickered across Akaashi’s face this time. Something that, even with his emotional illiteracy, looked something like hope. Akaashi was quiet for a few moments.

“What would you say,” he started quietly, “If I told you that Bokuto, Kuroo and I are in one relationship together?” Kei felt his heart stop and sink and his head cloud over. He was too late. They were already in a relationship. They didn’t need or want _him_.

“Congratulatio-,” he started, but Akaashi interrupted, looking him directly in the eye.

“If I told you that the three of us are in a relationship together, but that we’d like you to join us too.”

Kei felt his heart stop again.

“You - what,” he breathed. Akaashi didn’t break his eye contact. He didn’t give any indication that this was all a joke to him, that they were pulling his leg. His gaze didn’t break, and didn’t lose its intensity.

“You’re serious,” Kei breathed, more to himself, but Akaashi nodded anyway.

“We are.”

“Yes - I - I’d say yes, yes _please_.” Akaashi smiled at him.

“Good.”

Akaashi kissed him then, and Kei melted into him. He didn’t pay attention to what his hands were doing beyond them reaching for Akaashi, drawing him closer, carding through his hair. All he could pay attention to was the fact that _Akaashi_ was _kissing him_ , and that Kei had no idea if it was any good or not, but he didn’t want it to stop. Everything else faded into the background. He didn’t even notice Kuroo and Bokuto return from the bathroom until he felt hands, new hands, too large to be Akaashi’s, on his shoulders and in his hair.

Kei pulled away from Akaashi, and a few murmurs between the four of them later, and Kei officially had not one, not two, but _three_ boyfriends.

The rest of their practice session was soon forgotten in favour of sharing kisses with his new boyfriends.

When Kei finally entered the room Karasuno was staying in not long before lights out, Yamaguchi took one look at his face and smirked knowingly.

Kei threw a pillow in his face.

 

 

Yamaguchi forming a crush on Terushima Yuuji came as a surprise to both of them.

One match, a little flirting, and he’d suddenly become a stammering, red-faced mess at the mere mention of him.

At first, Kei thought that this would give him ammunition that would last him _months_ , and certainly, it had lasted him a good couple of weeks. Until Yamaguchi had literally collided with Terushima while out one day, and before Kei knew it, the two of them had been on a date, then another, and another, until a week before Kei's training camp, Yamaguchi admitted that Terushima had officially asked him out, and that he’d said yes. And he’d gone from the stammering, full-force-blushing Yamaguchi to one that just flushed. And occasionally ditched the team for post-practice meat buns to go on a date with his boyfriend.

Kei wasn’t sure exactly _when_ the team started to realise that _something_ was going on, but that was when he knew they’d noticed something. Kei could practically _hear_ Suga-san putting pieces together.

Yamaguchi had never failed to miss meat buns before, but he’d begged off the last three times because he _had plans_. Plans that very obviously didn’t include him. Kei, on the other hand, disappeared after practice during the training camps to go and practice with his boyfriends, and while they did practice, Kei always returned to his team in a much more ruffled state than he’d left them in. Kei and Yamaguchi didn’t have quite as many sleepovers together as they had done before, and while that could be explained away with separate practice sessions, or other excuses, half of the days they would have had a sleepover, Kei had been visiting or being visited by his boyfriends, or Yamaguchi had been spending time with his own. Kei had even missed an entire weekend of practice, including the Friday afternoon, a couple of weeks after the Miyagi finals to go and support his boyfriends in their own qualifier matches. Not that he’d told the team that. As far as _they_ knew, he’d been away with family, which from Kei’s point of view wasn’t exactly wrong.

Kei could think of two possible conclusions that Suga would jump to. Either they had broken up, or they were cheating on each other.

Kei told his boyfriends about it that night when he got home. They’d been getting regular updates of Yamaguchi’s relationship as it happened, and found the team’s obliviousness to be highly entertaining. Kuroo in particular, had been telling Kei that he and Yamaguchi should play into the assumed relationship, as a prank on the team. Kei had never bothered. That would take effort, and to be honest, they had never needed to.

 

 

This went on for a couple of weeks before the team, or rather, Sugawara, held an intervention.

“What’s going on with you two?” Suga demanded. Kei’s phone vibrated in his hand, and he frowned to himself. It wasn’t a meat bun night, and he’d told the others he’d be able to join their call, but practice had overrun a little, and now he and Yamaguchi had been taken hostage. Yamaguchi was fidgeting beside him. He had a date tonight, and if this went on for much longer, he’d miss his train.

Kei sent a message to the chat with his boyfriends.

 _We’ve been busted_ , he wrote, _I’ll call back when I’m free._

Suga went on, pointing out every little thing that had him worried about their relationship.

“Are you cheating on each other?”

_Ah, there it is._

Yamaguchi snorted.

Kei raised an eyebrow at him.

“Suga-san, that is the _furthest_ thing from the truth,” he laughed.

“Well what is it then?” Suga demanded. Yamaguchi turned to Kei.

“Kuroo-san and Yuuji were right, Tsukki. This is _hilarious_. We should have played around with it more.”

“For you, maybe. And since when’ve you and Kuroo been talking?”

“I told you about it _months_ ago, Tsukki-”

“ _Ahem_.” They turned back to Suga, who was watching them with his arms crossed and an eyebrow raised.

“You go on ahead,” Kei told Yamaguchi, “You don’t want to be late for you date. I’ll deal with this.”

“Thanks, Tsukki. See you later,” Yamaguchi slung his bags over his shoulder, and left with a wave, phone in hand and already dialling a number.

Kei’s phone buzzed in his hand again. The name _Bokuto Koutarou!!!! <3 <3_ flashed across the screen.

 _Of course it’s him_ , Kei thought wryly, _Always so impatient_.

Kei ignored it, and turned back to Suga.

“Yamaguchi has a date? And you know about it? Are you two in one of those open relationships?”

“No,” Kei replied.

“Then -”

“We’re not dating,” Kei told him, “We never have.”

“But I thought -”

“Yes, as did everyone. They’re just rumours.”

“So what about you? Are you dating anyone?”

“I think you know the answer to that.”

“But who? There are three possibilities.”

Kei didn’t answer.

“All three? People do that?”

“ _We_ do.”

Suga’s eyes widened.

“Oh. I didn’t know we could,” he said quietly, almost to himself.

 _Is Suga-san -_ Kei started to wonder, then cut his thoughts off. It wasn’t any of his business. And, unlike _some_ people, he didn’t like to _assume_ things.

“Can I go now?” he asked, as his phone buzzed in his hand again.

“Oh, yes, of course,” Suga replied distractedly, worlds away, “See you tomorrow, Tsukishima.”

Kei answered his phone the second he stepped outside.

“Hey, Bokuto.” He couldn’t resist his smile as Bokutou launched into conversation on the other end of the line.

Halfway home, he got a text sent to a new group chat between himself, Yamaguchi and Suga.

 

_Hey you two_

_Sorry for assuming you were in a relationship like everyone else, I should have asked first._

_Also as I’m the only one who knows the truth atm, how would you feel about seeing how long we can fool the rest of the team over this? @Yamaguchi, you were saying you wanted to be able to play around with it more so..??_

_Well I’ll leave it for you to decide_

_Hope you both have a great night_

 

Kuroo was going to _love_ this.

 

**Author's Note:**

> (They made it until Day 2 of Nationals until the rest of Karasuno found out what was going on.)
> 
> (Also if you haven't read 'unexpectedly' by avalescence_hurlocked then you really, really should. It's the fic that officially added Teruyama to my ships and is wonderful.)
> 
> Thanks for reading! <3
> 
> EDIT: I realised that the timings don't really work out, this has been corrected now! (Also I can't believe the reception this has gotten, thank you everyone so much! <3)


End file.
